| Solid state imaging device -> Monitor Keywords |
|
|
 
Solid state imaging deviceRelated Patent Categories: Radiant Energy, Photocells; Circuits And Apparatus, Photocell Controlled Circuit, Plural Photosensitive Image Detecting Element ArraysSolid state imaging device description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070145241, Solid state imaging device. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a solid state imaging device with excellent focusing efficiency. BACKGROUND OF THE INVENTION [0002] Recently, digital cameras are widely used which convert images, captured by a solid state imaging device such as CCD, into digital image data and store the data in recording media, such as an internal memory and a memory card. In order to facilitate focusing light rays on light receiving elements, such as photodiodes arranged in a matrix, the solid state imaging device in such digital cameras is generally equipped with microlenses located above the light receiving elements. [0003] FIG. 7 illustrates a structure in cross section of a conventional CCD. In FIG. 7, a CCD 100 includes a semiconductor substrate 102 with photodiodes 101 formed therein, a transparent insulating film 103 on a top surface of the semiconductor substrate 102, transfer electrodes 104 next to each line of the photodiodes 101, a light shielding layer 105 to cover the transfer electrodes 104 for light protection and having openings 106 above each photodiode 101, a planarizing layer 107 with a flat top surface for covering over the light shielding layer 105 and the photodiodes 101, a color filter 108 on the planarizing layer 107, and a microlens array 109 above the color filter 108 aligned such that microlenses 109a are located above each photodiode 101. In the CCD 100, a light ray is converged by the microlens 109a and received by the photodiode 101, which generates an electric charge proportional to the amount of light received. The generated electric charge is then transferred as a signal charge in a vertical direction by the transfer electrodes 104. The microlens array 109 is a transparent material layer on the color filter 108 and has microlenses 109a shaped by, for example, a dry etching technique. [0004] Unfortunately, the present-day dry etching techniques hardly put all the microlenses 109a into exactly the same shape. As a result, an efficiency for focusing light ray (i.e., focusing efficiency) varies among the microlenses 109. Additionally, the solid state imaging devices are becoming even smaller yet hold more pixels in these days, and the photodiodes are getting smaller in dimension. There is therefore a need to focus incident light rays effectively on the photodiodes. Accordingly, Japanese Patent Laid-open Publication No. 2001-44406 discloses a solid state imaging device which has a condensing lens directly above a light receiving part. Furthermore, Japanese Patent Laid-open Publication No. 2000-150845 discloses a solid state imaging device which has a well-form trench structure that directs a light ray from a color filter to a light receiving part. These components serve to prevent deterioration of the focusing efficiency due to variation in shape of the microlenses. [0005] However, even these solid state imaging devices cannot provide sufficient focusing efficiency and sometimes cause smear noise that appears as a vertical whitish line on a captured image. Rightly, an incident light ray from the microlens 109a should be directed to the opening 106 of the light shielding layer 105 and reach the photodiode 101. Insufficient focusing, however, allows some of the incident light rays to go toward the light shielding layer 105. Hardly does the light shielding layer 105 provide an absolute light shielding function, such an incident light ray, if it is intense enough, can permeate the transfer electrode 104 and reach a charge transfer section 110 where the incident light ray is converted into an electric charge. This electric charge saturates the signal charge in the charge transfer section 110 and causes the smear noise. [0006] Another disadvantage of the Japanese Patent Laid-open Publication No. 2001-44406 is that the condensing lens above the light receiving part has a lower refractive index than the surrounding planarizing layer. This configuration makes the light rays proceeding form a flattening, or planarizing, layer toward the condensing lens more likely to diffuse and may possibly deteriorate the focusing efficiency. Another disadvantage of the Japanese Patent Laid-open Publication No. 2000-150845 is the formation of the well-form trench structure that extends from the microlens toward the light receiving part. Such a trench structure is very difficult to form in modern solid state imaging devices that are so small in dimension. As a result, voids and other defects are more likely to occur, and effective focusing of light rays on the light receiving part is hardly achieved. SUMMARY OF THE INVENTION [0007] In view of the foregoing, a primary object of the present invention is to provide a solid state imaging device to improve an efficiency for focusing light rays toward light receiving elements in a semiconductor substrate. [0008] Another object of the present invention is to provide a solid state imaging device to prevent light rays from heading to transfer electrodes and avoid an occurrence of smear noise. [0009] In order to achieve the above and other objects, the solid state imaging device according to the present invention includes a semiconductor substrate, a light shielding layer, a planarizing layer, microlenses, and a converging structure. Formed in the semiconductor substrate are light receiving elements and vertical transfer paths for transferring electric charges accumulating in the light receiving elements. Provided on the semiconductor substrate is the light shielding layer, which covers the vertical transfer paths for protection from light and has openings formed at positions corresponding to the light receiving elements. The light shielding layer and the light receiving elements are covered by the plarnarizing layer, above which the microlenses are disposed to focus light toward the light receiving elements. The converging structure is provided inside each opening and has a higher refractive index than the surrounding medium such as, for example, the plarnarizing layer. [0010] It is preferable that the converging structure satisfies an equation of D=(.lamda./n.sub.2){1/4+N/2}, where D is a thickness of a centre portion of the converging sturucture, .lamda. is a wavelength of light entering the converging structure, and N is an integer. The converging structure is either a plano-convex lens, a rectangular solid block, or a plano-concave lens. more preferably, the refractive index of the converging structure is gradually decreasing from the center toward the edge. When the converging structure is the rectangular solid block or the plano-concave lens, the converging structure preferably have an outer circumference smaller than the opening. It is more preferable in this case to provide an anti-reflection film between each converging structure and photodiode. Favorably, the anti-reflection film satisfies the equations of D=(.lamda./n.sub.2){1/4+N/2}, where D is a thickness of a centre portion of the anti-reflection film, .lamda. is a wavelength of light entering the anti-reflection film, and N is an integer. [0011] According to the solid state imaging device of the present invention, the covering structure that has a higher refractive index than the surrounding medium is provided inside each of the openings for the photodiodes. This configuration improves the efficiency for focusing light toward the light receiving elements. It is therefore possible to prevent light from permeating transfer electrodes, and smear noise is prevented. [0012] Since the converging structure is appropriately adjusted in shape, refractive index, and center portion's thickness, the focusing efficiency is more improved. In accordance with the embodiment using the anti-reflection film between the converging structure and the photodiode, reflection of the incident light is prevented effectively and the focusing efficiency is even more improved. BRIEF DESCRIPTION OF THE DRAWINGS [0013] The above objects and advantages of the present invention will become more apparent from the following detailed description when read in connection with the accompanying drawings, in which: [0014] FIG. 1 is an explanatory view of a solid state imaging device according to a first embodiment of the present invention; [0015] FIG. 2 is a cross sectional view along a line II-II of FIG. 1; [0016] FIG. 3 is an enlarged cross sectional view around a converging structure; [0017] FIG. 4 is a cross sectional view of a solid state imaging device according to a second embodiment of the present invention, where a rectangular solid block is employed as the converging structure; [0018] FIG. 5 is a cross sectional view of a solid state imaging device according to a third embodiment of the present invention, where a plano-concave lens is employed as the converging structure; [0019] FIG. 6 is a cross sectional view of a variant of the second embodiment, where an anti-reflection film is formed between the converging structure and the photodiode; and [0020] FIG. 7 is a cross sectional view of a conventional solid state imaging device. Continue reading about Solid state imaging device... Full patent description for Solid state imaging device Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Solid state imaging device patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Solid state imaging device or other areas of interest. ### Previous Patent Application: Semiconductor imaging device Next Patent Application: Image sensor Industry Class: Radiant energy ### FreshPatents.com Support Thank you for viewing the Solid state imaging device patent info. IP-related news and info Results in 0.36806 seconds Other interesting Feshpatents.com categories: Tyco , Unilever , Warner-lambert , 3m 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
